Automobile-based collision airbags are designed to deploy in frontal and near-frontal collisions more severe than a threshold defined by the regulations governing vehicle construction in whatever particular market the vehicle is intended for. For example, United States government regulations require deployment in crashes at least equivalent in deceleration to a 23 km/h (14 mph) barrier collision, or similarly, striking a parked car of similar size across the full front of each vehicle at about twice the speed. However, many international regulations are performance based, rather than technology-based, so airbag deployment threshold is a function of overall vehicle design.
Most people are familiar with crash tests associated with direct frontal collisions. However, unlike crash tests into barriers, real-world crashes typically occur at angles other than directly into the front of the vehicle, and the crash forces usually are not evenly distributed across the front of the vehicle. Consequently, the relative speed between a striking and struck vehicle required to deploy the airbag in a real-world crash can be much higher than an equivalent barrier crash. Many sensors used in airbag systems employ a plurality of MEMS accelerometers, which are small integrated circuits with integrated micro mechanical elements that are responsive to rapid deceleration. In earlier airbag systems, some attempts were made to use mercury switches, without much success. In other early systems, a plurality of mechanical “rolamite” devices, which are low-friction rollers suspended in a tensioned band, were used to detect sudden changes in momentum along predetermined axes.
In the case of systems using macro-mechanical sensors, it would be advantageous to have a single sensor device that can effectively detect sudden changes in momentum that exceed a predetermined threshold over multiple axes, and as a result facilitate external electrical signals that can be converted into practical uses, such as the strategic automatic deployment of automobile air bags.